1. Field of the Invention
The present invention generally relates to fabrication of integrated circuits in the semiconductor industry.
2. Discussion of the Background
The fabrication of integrated circuits (IC) in the semiconductor industry typically employs plasma to create and assist surface chemistry within a plasma processing chamber necessary to remove material from and deposit material to a substrate. In general, plasma is formed within the processing chamber under vacuum conditions by heating electrons to energies sufficient to sustain ionizing collisions with a supplied process gas. Moreover, the heated electrons can have energy sufficient to sustain dissociative collisions and, therefore, a specific set of gases under predetermined conditions (e.g., chamber pressure, gas flow rate, etc.) are chosen to produce a population of charged species and chemically reactive species suitable to the particular process being performed within the chamber (e.g., etching processes where materials are removed from the substrate or deposition processes where materials are added to the substrate).
The semiconductor industry is constantly striving to produce smaller ICs and to increase the yield of viable ICs. Accordingly, the material processing equipment used to process the ICs have been required to meet increasingly more stringent performance requirements for etching and deposition processes (e.g., rate, selectivity, critical dimension, etc.).
The reproducibility of plasma processing operations can be assured if it is verified that important plasma parameters (e.g., plasma density) have values that lie between predetermined limits. Furthermore, it is most advantageous to be able to make such determinations using a real time measurement technique.
The electromagnetic behavior of a plasma provides useful information about the state of the plasma. For example, the emission and absorption of optical and/or infrared radiation, and the transmission/absorption of microwave radiation through a plasma are indicators of the plasma state. The present invention provides microwave techniques for the measurement of plasma density and the use of data obtained from such measurements may be used to control plasma properties by means of the automatic adjustment of RF power, pressure, gas composition, etc. The present invention relates to a method and apparatus for determination and control of a plasma state within a plasma chamber. The present invention advantageously provides a method and apparatus that enables semiconductor manufacturers to satisfy more stringent performance requirements for material processing equipment used in the semiconductor industry.
The present invention advantageously provides a first embodiment of a plasma processing system that includes a plasma chamber, an open resonator movably mounted within the plasma chamber, and a detector. The open resonator is configured to produce a microwave signal, and the detector is configured to detect the microwave signal and measure a mean electron plasma density along a path of the microwave signal within a plasma field of the plasma chamber. The plasma processing system preferably further includes a processor configured to receive a plurality of mean electron plasma density measurements from the detector that correspond to a location of the open resonator.
The processor is preferably configured to calculate plasma density within the plasma field as a function of position using the plurality of mean electron plasma density measurements. For example, the processor is configured to utilize tomographic inversion to calculate plasma density as a function of position using the plurality of mean electron plasma density measurements. The processor is configured to calculate plasma density as a function of position and determine whether a plasma density at a given location is within a predetermined range. The processor is configured to ensure that the plasma density at the given location is within the predetermined range. The processor is configured to control plasma properties by at least one of adjusting RF power, adjusting pressure within the plasma chamber, and adjusting gas composition within the plasma chamber.
The present invention further advantageously provides a second embodiment of a plasma processing system that includes a plasma chamber, a plurality of open resonators provided within the plasma chamber, a plurality of detectors, and a processor. The plurality of open resonators are configured to produce microwave signals, and the plurality of detectors are configured to detect the microwave signals and measure a mean electron plasma density along paths of the microwave signals within a plasma field of the plasma chamber. The processor is configured to receive a plurality of mean electron plasma density measurements from the detectors that correspond to locations of the plurality of open resonators.
The present invention additionally provides a method for controlling a plasma state within a plasma chamber. The method includes the steps of measuring mean electron plasma density along a path at a plurality of locations within a plasma field in the plasma chamber, and calculating plasma density within the plasma field as a function of position using the measured mean electron plasma density.
In a first embodiment of the method, the step of measuring mean electron plasma density preferably includes the steps of providing an open resonator that is movably mounted within the plasma chamber, where the open resonator is configured to produce a microwave signal, and detecting the microwave signal to measure the mean electron plasma density. In a second embodiment of the method, the step of measuring mean electron plasma density preferably includes the steps of providing a plurality of open resonators within the plasma chamber, where the plurality of open resonators are configured to produce microwave signals, and detecting the microwave signals to measure a mean electron plasma density along paths of the microwave signals within a plasma field of the plasma chamber.